1. Field of the Invention
This invention relates to a robot controller for controlling an industrial robot (hereinafter referred to as “robot”). More specifically, the invention relates to a robot controller for stopping a robot based on the speed of a robot hand portion.
2. Description of the Related Art
A robot used in a factory or the like may undergo an abnormal operation, due to abnormal hardware or software. However, it is an accepted practice to bring the robot into an emergency stop when the robot undergoes an abnormal operation.
Japanese Unexamined Patent Publication JP-A-6-91587 discloses a technology, which determines if the robot is in an abnormal situation when either the acceleration or the speed of the end portion of the robot arm becomes greater than a predetermined value. Japanese Unexamined Patent Publication JP-A-10-264080 discloses that if the robot is abnormally operating by comparing an index periodically prepared for detecting abnormal condition such as the moving speed of the tool end point of the robot with a reference value. According to JP-A-6-91587 and JP-A-10-264080, the robot is stopped when abnormal operation of the robot is detected.
A robot of the type of the top mount loader includes a traveling rail supported by struts and extending in a horizontal direction, and a robot body attached to a slider that slides on the traveling rail. The robot body has a robot hand portion at an end thereof. In the robot of the type of the top mount loader as described above, there is a case in which the robot body should move at a high speed along the traveling rail but is not required to move at a high speed in a direction perpendicular to the traveling rail.
However, it is not proper to exclude the probability of motion of the robot body in the direction perpendicular to the traveling rail by taking the safety into consideration. Therefore, the struts supporting the traveling rail should be strength enough to withstand a maximum speed of the robot body. However, fabricating the struts so as to withstand the maximum speed of the robot body involves a problem of an increase in the cost of producing the struts and the robot.
On the contrary, it is also allowable to adjust the robot so that it cannot exhibit its dynamic capability to its maximum degree in order to lower the strength required for the struts. However, this also results in a decrease in the moving speed of the robot of the type of the top mount loader along the traveling rail, which is the most important requirement. If the dynamic capability of the robot is limited in advance, therefore, there often occurs such a situation that the robot is not capable of effecting the operation practically required on the spot such as in the factory or the like place.
This invention was achieved in view of the above-mentioned circumstances and has an object of providing a robot controller which makes it possible to lower the strength required for the struts without limiting the dynamic capability of the robot.